1. Field of the Invention:
The present invention relates generally to the production of slide fasteners, and more particularly to an apparatus for forming a row of coupling elements for slide fasteners on a rotating die wheel.
2. Description of the Prior Art:
Canadian Pat. No. 669,722 and Japanese Patent Laid-Open Publication No. 59-125506 disclose a coupling-element forming apparatus which comprises a heated die wheel having an annular central groove in its peripheral surface and a pair of rows of circumferentially staggered pins disposed one row on each side of the groove. In this prior apparatus, a monofilament of thermoplastic synthetic resin is wound around the pins on the peripheral surface of the rotating die wheel, and then it is forced into the groove so as to be folded into a succession of U-shaped coupling element blanks, and subsequently the successive U-shaped coupling element blanks are shaped into a final shape as their lower turned portions are deformed by a punch linearly movable into the groove. A primary problem with the known apparatus is that because the punch moves linearly, as shown in FIG. 10 of the accompanying drawings, the coupling heads 9a would be shaped as objectionably flowed to one side, if the die wheel is continuously rotated during the shaping of the coupling heads 9a. Such objectionably deformed coupling heads 9a would impede correct coupling of the resulting coupling elements 12'. In order to avoid such objectionably deformed coupling heads, the die wheel of the known apparatus must be rotated intermittently as the punch reciprocates into and out of the groove. Because of this intermittent rotation of the die wheel, an adequate rate of production cannot be achieved.